5G networks aim for a speed of a few Gbit/s and latencies of the order of a millisecond as well as a high capacity in Gbit/s per cell, while limiting energy consumption. These objectives require modifying the radio interface of 5G networks compared to that of 4G networks. The choice was made to use the same architectural principles of the radio access network and to keep the transmission on orthogonal sub-carriers or Orthogonal Frequency Division Multiplexing (OFDM) to facilitate the transition from 4G to 5G. On the other hand, the possible settings are much more numerous both in the frequency domain and in the time domain. An important feature of the 5G-NR air interface is that it is designed to allow the use of antenna arrays that can be used to both focus radiation in the direction of interest (beamforming) and to allow transmissions of different streams on the same time-frequency resource, principle of the techniques Multiple-Input-Multiple-Output (MIMO).
The objective of this article is to expose the essential principles of the 5G radio interface, called New Radio (NR) and to show how the choices made make it possible to achieve the targeted objectives. After a presentation of the physical and protocol architecture, it reviews the general principles of transmission and allocation and introduces multi-antenna technologies. It addresses the frequency organization, which makes it possible to deduce the order of magnitude of the achievable speeds according to the different frequency ranges, then the temporal organization to underline the influence on the latency. It explains how the beacon channel is organized to reduce energy consumption and authorize the formation of beams, then how the access mechanisms are consistent with this organization. It concludes with a presentation of the control functions on an established radio link and in particular on the main reference signals inserted in the transmission which are essential for this control.
